This invention relates to a method of making an inflatable intramedullary bone canal plug for plugging an open-ended intramedullary canal of a bone which is capable of restricting the flow of bone cement after inflation, particularly during the pressurized injection of bone cement, during a procedure involving the implantation of a joint prosthesis to the end of a bone and to the bone plugs made by that method. The bone plug prepared by this method is further capable of deflating in a relatively short period of time after the cement hardens to avoid possible weakening of the cortical bone surrounding the inflated bone plug.
Degenerative bone diseases and injuries to the joints often make it necessary or desirable to replace the natural joint with an artificial prosthesis. One such replacement involves the fixation of an artificial hip joint prosthesis to the proximal end of the femur. The femur contains a hollow intramedullary bone canal running through its central long axis. It is desirable to affix a hip joint prosthesis to the femur in such a manner that the stem of the prosthesis lies along the central long axis of the femur. In preparing the proximal end of the femur to receive such a prosthesis, an appropriately sized opening to receive the stem of the prosthesis is made in the proximal end of the femur. That opening normally extends into the intramedullary bone canal approximately along the central long axis of the femur and is wide enough to permit bone cement to be compacted about the stem to secure the prosthesis to the femur.
To prevent bone cement from flowing deeper into the intramedullary bone canal than is necessary, an intramedullary bone canal plug ("bone plug") composed of a piece of the removed femur or a plug of partially cured bone cement has been used to restrict the flow of cement. Likewise various bone plugs having sides which press-fit against the cortical bone forming the canal to form a seal have been proposed in U.S. Pat. Nos. 4,245,359 (Stuhmer, issued Jan. 20, 1981); 4,302,855 (Swanson, issued Dec. 1, 1981) and 4,293,962 (Fuson, issued Oct. 13, 1981). Once in place, press-fit plugs are difficult to remove and if they do not fit tightly enough, the plug can be driven further down the intramedullary canal when cement is injected under pressure. See U.S. Pat. Nos. 4,462,394 (Jacobs, issued July 31, 1984); 4,357,716 (Brown, issued Nov. 9, 1982) and 3,889,665 (Ling, et al.) for examples of pressurized injection of bone cement.
In U.S. Pat. No. 4,344,190 (issued Aug. 17, 1982), Lee, et al. teach a biodegradeble press-fit bone plug which serves to block the flow of bone cement, but later degrades to alleviate pressure against the hard cortical bone forming the intramedullary canal caused by press-fitting the plug in the canal. As a result, the risk of a fracture occurring at the bone plug site is said to be reduced. No mention is made as to the length of time required before a sufficient level of resorption of the plug occurs to release the pressure. Furthermore, there is no way to adjust to tightness of fit other than by plug size selection. Once inserted, the plug appears to be difficult to remove and, once inserted, a less than optimally-fitting plug could be driven deeper into the canal by the pressure of the cement being injected.
One bone plug designed to be securely fastened inside of the intramedullary bone canal is taught in U.S. Pat. No. 4,447,915 (Weber, issued May 15, 1984). The Weber Patent teaches a two piece medullary bone canal plug formed by a deformable and expandable outer body having a jacket formed of a number of segments and a conical expansion body which is pulled into the outer body to expand the outer body. Once pulled together, the two bodies are permanently secured together via serrations of the inside of the outer body and the outside of the expansion body. However, it appears that once the two bodies are secured together, the plug cannot be removed if for some reason that should become desirable. Likewise, if the plug is secured so that too much pressure is exerted against the sides of the intramedullary bone canal, the presence of the plug may increase the risk of fracture as noted in the Lee, et al. Patent above.
None of the above bone plugs are inflatable.